1. Field of the Invention
An exemplary embodiment of the invention relate to a liquid crystal display and a method of driving the same.
2. Discussion of the Related Art
Active matrix type liquid crystal displays display a moving picture using a thin film transistor (TFT) as a switching element. The active matrix type liquid crystal displays have been implemented in televisions as well as display devices in portable devices, such as office equipment and computers, because of the thin profile of the active matrix type liquid crystal displays. Accordingly, cathode ray tubes (CRT) are being replaced by active matrix type liquid crystal displays.
As shown in FIG. 1, a test pattern may be used in an inspection process for inspecting the image quality of a liquid crystal display. In the inspection process, after a striped pattern, in which pixels charged to a white gray level voltage and pixels charged to a black gray level voltage are alternately positioned, is applied to the liquid crystal display and the liquid crystal display displays the striped pattern for a predetermined period of time, a voltage applied to pixels in a middle area of a display screen of the liquid crystal display is adjusted at an intermediate gray level voltage between the white gray level voltage and the black gray level voltage. As a result, a common voltage shifts depending on a location of the screen, and thus crosstalk occurs. This is because the common voltage applied to a common electrode of a liquid crystal cell shifts depending on changes in a data voltage applied to a pixel electrode of the liquid crystal cell by a coupling between the pixel electrode and the common electrode.
A polarity of the data voltage applied to the liquid crystal display is periodically inverted so as to suppress a direct current (DC) drive of a liquid crystal. When the liquid crystal display displays the test pattern shown in FIG. 1, polarities of the data voltages are shown in FIG. 2. FIG. 2 shows polarities of the data voltages in a portion of the test pattern of FIG. 1. The data voltages of the test pattern are inverted according to a horizontal and vertical 1 dot inversion scheme used when a general image is input. In the horizontal and vertical 1 dot inversion scheme, polarities of the data voltages supplied to neighboring liquid crystal cells in a horizontal direction are opposite to each other, and polarities of the data voltages supplied to neighboring liquid crystal cells in a vertical direction are opposite to each other. If polarities of the data voltages of the test pattern shown in FIG. 1 are inverted according to the horizontal and vertical 1 dot inversion scheme, a greenish phenomenon in which green cells are brightly seen occurs, and a luminance difference between neighboring lines occurs. This is because the polarities of the data voltages charged to the liquid crystal display lean to any one polarity. This will be described with reference to FIGS. 3 and 4.
As shown in FIG. 3, in the pixels on A-line to which the white data voltage is applied, polarities of R-data voltage and B-data voltage are a positive polarity, and a polarity of G-data voltage is a negative polarity. Accordingly, in the A-line, the positive data voltage is more dominant than the negative data voltage. As a result, a ripple of a common voltage Vcom in the A-line increases toward a positive polarity, and thus the common voltage Vcom shifts toward the positive polarity. Further, because the G-data voltage, that is applied as a positive black voltage +Vblack during a previous frame period, changes to a negative white voltage −Vwhite during a current frame period, a voltage difference between the G-data voltages during the neighboring frame periods increases. Therefore, the greenish phenomenon appears.
As shown in FIG. 4, in the pixels on B-line to which the white data voltage is applied, polarities of the R-data voltage and the B-data voltage are a negative polarity, and a polarity of the G-data voltage is a positive polarity. Accordingly, in the B-line, the negative data voltage is more dominant than the positive data voltage. As a result, a ripple of the common voltage Vcom in the B-line increases toward a negative polarity, and thus the common voltage Vcom shifts toward the negative polarity. Further, because the G-data voltage, that is applied as a negative black voltage −Vblack during a previous frame period, changes to a positive white voltage +Vwhite during a current frame period, a voltage difference between the G-data voltages during the neighboring frame periods increases. Therefore, the greenish phenomenon appears.
When the data voltages (for example, the white voltage and the black voltage) with a large voltage difference therebetween are applied to the neighboring pixels, the greenish phenomenon, a smear phenomenon, and the crosstalk occur in the related art liquid crystal display because the data voltages lean to any one polarity. Accordingly, the display quality of the related art liquid crystal display is reduced in the data of some weak patterns.